Re: [PATCH RESEND v6 01/36] memory: alloc RAM from file at offset

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Apr 22, 2020 at 09:13:36PM -0700, elena.ufimtseva@oracle.com wrote:
> From: Jagannathan Raman <jag.raman@oracle.com>
> 
> Allow RAM MemoryRegion to be created from an offset in a file, instead
> of allocating at offset of 0 by default. This is needed to synchronize
> RAM between QEMU & remote process.

Can you elaborate on why remote processes require the RAM to be offset
from zero ?

NB, I'm not objecting - I'm just curious to understand more.

> 
> Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
> Signed-off-by: John G Johnson <john.g.johnson@oracle.com>
> Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
>  exec.c                    | 11 +++++++----
>  include/exec/ram_addr.h   |  2 +-
>  include/qemu/mmap-alloc.h |  3 ++-
>  memory.c                  |  2 +-
>  util/mmap-alloc.c         |  7 ++++---
>  util/oslib-posix.c        |  2 +-
>  6 files changed, 16 insertions(+), 11 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index 2874bb5088..d0ac9545f4 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -1801,6 +1801,7 @@ static void *file_ram_alloc(RAMBlock *block,
>                              ram_addr_t memory,
>                              int fd,
>                              bool truncate,
> +                            off_t offset,
>                              Error **errp)
>  {
>      void *area;
> @@ -1851,7 +1852,8 @@ static void *file_ram_alloc(RAMBlock *block,
>      }
>  
>      area = qemu_ram_mmap(fd, memory, block->mr->align,
> -                         block->flags & RAM_SHARED, block->flags & RAM_PMEM);
> +                         block->flags & RAM_SHARED, block->flags & RAM_PMEM,
> +                         offset);
>      if (area == MAP_FAILED) {
>          error_setg_errno(errp, errno,
>                           "unable to map backing store for guest RAM");
> @@ -2283,7 +2285,7 @@ static void ram_block_add(RAMBlock *new_block, Error **errp, bool shared)
>  #ifdef CONFIG_POSIX
>  RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
>                                   uint32_t ram_flags, int fd,
> -                                 Error **errp)
> +                                 off_t offset, Error **errp)
>  {
>      RAMBlock *new_block;
>      Error *local_err = NULL;
> @@ -2328,7 +2330,8 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
>      new_block->used_length = size;
>      new_block->max_length = size;
>      new_block->flags = ram_flags;
> -    new_block->host = file_ram_alloc(new_block, size, fd, !file_size, errp);
> +    new_block->host = file_ram_alloc(new_block, size, fd, !file_size, offset,
> +                                     errp);
>      if (!new_block->host) {
>          g_free(new_block);
>          return NULL;
> @@ -2358,7 +2361,7 @@ RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
>          return NULL;
>      }
>  
> -    block = qemu_ram_alloc_from_fd(size, mr, ram_flags, fd, errp);
> +    block = qemu_ram_alloc_from_fd(size, mr, ram_flags, fd, 0, errp);
>      if (!block) {
>          if (created) {
>              unlink(mem_path);
> diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
> index 5e59a3d8d7..1b9f489ff0 100644
> --- a/include/exec/ram_addr.h
> +++ b/include/exec/ram_addr.h
> @@ -121,7 +121,7 @@ RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
>                                     Error **errp);
>  RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
>                                   uint32_t ram_flags, int fd,
> -                                 Error **errp);
> +                                 off_t offset, Error **errp);
>  
>  RAMBlock *qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
>                                    MemoryRegion *mr, Error **errp);
> diff --git a/include/qemu/mmap-alloc.h b/include/qemu/mmap-alloc.h
> index e786266b92..4f579858bc 100644
> --- a/include/qemu/mmap-alloc.h
> +++ b/include/qemu/mmap-alloc.h
> @@ -25,7 +25,8 @@ void *qemu_ram_mmap(int fd,
>                      size_t size,
>                      size_t align,
>                      bool shared,
> -                    bool is_pmem);
> +                    bool is_pmem,
> +                    off_t start);
>  
>  void qemu_ram_munmap(int fd, void *ptr, size_t size);
>  
> diff --git a/memory.c b/memory.c
> index 601b749906..f5fec476b7 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -1596,7 +1596,7 @@ void memory_region_init_ram_from_fd(MemoryRegion *mr,
>      mr->destructor = memory_region_destructor_ram;
>      mr->ram_block = qemu_ram_alloc_from_fd(size, mr,
>                                             share ? RAM_SHARED : 0,
> -                                           fd, &err);
> +                                           fd, 0, &err);
>      mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;
>      if (err) {
>          mr->size = int128_zero();
> diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
> index 27dcccd8ec..a28f7025f0 100644
> --- a/util/mmap-alloc.c
> +++ b/util/mmap-alloc.c
> @@ -86,7 +86,8 @@ void *qemu_ram_mmap(int fd,
>                      size_t size,
>                      size_t align,
>                      bool shared,
> -                    bool is_pmem)
> +                    bool is_pmem,
> +                    off_t start)
>  {
>      int flags;
>      int map_sync_flags = 0;
> @@ -147,7 +148,7 @@ void *qemu_ram_mmap(int fd,
>      offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr;
>  
>      ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE,
> -               flags | map_sync_flags, fd, 0);
> +               flags | map_sync_flags, fd, start);
>  
>      if (ptr == MAP_FAILED && map_sync_flags) {
>          if (errno == ENOTSUP) {
> @@ -172,7 +173,7 @@ void *qemu_ram_mmap(int fd,
>           * we will remove these flags to handle compatibility.
>           */
>          ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE,
> -                   flags, fd, 0);
> +                   flags, fd, start);
>      }
>  
>      if (ptr == MAP_FAILED) {
> diff --git a/util/oslib-posix.c b/util/oslib-posix.c
> index 062236a1ab..4c6b9e90c6 100644
> --- a/util/oslib-posix.c
> +++ b/util/oslib-posix.c
> @@ -209,7 +209,7 @@ void *qemu_memalign(size_t alignment, size_t size)
>  void *qemu_anon_ram_alloc(size_t size, uint64_t *alignment, bool shared)
>  {
>      size_t align = QEMU_VMALLOC_ALIGN;
> -    void *ptr = qemu_ram_mmap(-1, size, align, shared, false);
> +    void *ptr = qemu_ram_mmap(-1, size, align, shared, false, 0);
>  
>      if (ptr == MAP_FAILED) {
>          return NULL;
> -- 
> 2.25.GIT
> 

Regards,
Daniel
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